To raise and lower terrain, both the Flatten Vertices and Soften Vertices boxes should be unchecked. The Edit Colors box should also be unchecked.
Not sure if yours is the same problem, but whenever my Landscape Editor doesn't work (raising/lowering terrain or adding textures), it's always because I am near the cutoff of the loaded cells. To my knowledge, the CS can only load a certain number of cells at a time to work on, and when you try to use the Landscape Editor in cells near the cutoff, it doesn't work. Everything else does, but you can't do anything with terrain or textures.
If you hit the "B" key, it will toggle on/off your cell grid lines (yellow dashed lines). Pan over a cell or two in each direction to see if the world suddenly cuts off at one of the grid lines, leaving only a blue-gray void on the other side. IF this is your problem, you should see that cutoff somewhere near where you are trying to raise the land. If not, then this may be something else. Might be worth a try to see if it is.
If it is, you have to force the CS to load the cells beyond the cutoff. My somewhat crude solution is to drag some object from an adjacent visible cell - preferably something big, like a tree - past the cutoff and into the void area, which forces those cells to load (sometimes takes several seconds). Then alt-Z (or click undo) to move the object back to its original location. Once the adjacent cells are loaded, you should be able to use the Landscape Editor in the location you want. If you are in the middle of nowhere and there are no objects to drag, you will have to add something first (e.g. a tree) and then drag that. Just don't forget to delete it after the other cells load. I'm sure there's a more elegant (maybe easier) way of doing this, but this method always works for me.